2002 Fiscal Year Final Research Report Summary
Nonlinear Dynamics of Microbubbles and Its Influence on a Tissue Surface
| Project/Area Number |
12650177
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Fluid engineering
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| Research Institution | Osaka Prefecture University |
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Principal Investigator |
TAKAHIRA Hiroyuki Osaka Prefecture Univ., Dep. of Energy Systems Eng., Associate Prof., 工学研究科, 助教授 (80206870)
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| Project Period (FY) |
2000 – 2002
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| Keywords | Microbubble / Toroidal Bubble / Laser Trapping / Boundary Element Method / Heat Transfer / Compliant Boundary / Gas Diffusion / Surface Tension |
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| Research Abstract |
1. Analysis for the dynamics of microbubbles using laser trapping method
We applied a laser trapping method to investigate the microbubble dynamics experimentally. The results are summarized as follows:
(1) We measured optical trapping forces acting on microbubbles. The vertical force was about 90 pN under the net laser power of 110mW.
(2) The simulated trajectories of microbubbles were in good agreements with experiments.
(3) We performed the laser trapping near a solid boundary and simulated the bubble trajectories that escaped from the laser trap in a shear flow. The trajectory was much dependent of bubble radii.
(4) We investigated the influence of gas diffusion and surface tension on the stability of microbubbles. It was shown that the surface tension of microbubbles for ultrasonography was about 800 times smaller than the air-water bubble. When the radii of trapped or merged microbubbles were larger than a critical bubble radius that was determined from the surface tension and the concentration of dissolved gas, the bubbles grew rapidly.
2. Numerical analysis for the collapse of microbubbles with the boundary element method.
We developed a numerical method to compute the toroidal bubble dynamics by considering the heat transfer of internal gas. We applied this method to the bubble collapse near a solid wall or a deformable wall that represents the tissue surface. The results are summarized as follows:
(1) The microbubble collapse is accelerated due to the heat transfer of internal gas. After the liquid-jet threads the bubble surface, extremely high-pressure area is observed around the jet-impact point.
(2) The effective polytropic index for thermal diffusivity is useful to predict bubble motions qualitatively. However, to evaluate the maximum wall pressure, we need to deal with the heat transfer directly.
(3) The condition of the neutral collapse for bubble translation is much dependent on the thermal diffusion of internal gas.
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